1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device which can be made thinner than conventional semiconductor devices and enables high-density mounting, and can be produced by a simple production process.
2. Description of the Related Art
Conventionally known semiconductor devices which enables high-density mounting include those having a Multi-Chip-Package (hereinafter referred to as “MCP”) structure, in which a plurality of chips are mounted in a single package.
For example, in a 2-chip lamination type MCP, when two chips having the same or almost the same chip size are laminated, a lower chip is fixed on a substrate with an adhesive, a spacer such as a silicon piece or a piece of tape is fixed on the lower chip with an adhesive, and then, wires connecting the lower chip to bonding posts on the substrate are provided by wire bonding. Subsequently, an upper chip is fixed on the spacer with an adhesive, and wires connecting the upper chip to bonding posts on the substrate are provided by wire bonding. Then, the lower chip, the upper chip and the wires are sealed with a resin, and external terminals are attached to a back surface of the substrate.
However, since the spacer is used in such MCPs, the structure thereof becomes triple layer structure. This increases the thickness of the entire package, as well as assembly steps, material costs and assembly costs.
An example of a semiconductor device having the MCP structure which has solved the above-described problem is described in Japanese Patent Application Laid-Open (JP-A) No. 2002-124625.
In the semiconductor device described in the above patent document, an opening is formed in the substrate, and a lower chip is accommodated in the opening with its front surface facing down. On a back surface of the lower chip, a back surface of an upper chip, which has, for example, the same or almost the same size as the lower chip, is fixed. Wires connecting the upper chip to bonding posts on the front surface of the substrate are provided by wire bonding, and the upper chip and the wires are sealed with a resin. Terminals are disposed on a back surface of the substrate, and the terminals are electrically connected to the bonding posts at the front surface via through holes.
In such MCPs, two chips, which have the same or almost the same chip size, can be laminated without use of a spacer therebetween. Therefore, the above-described drawback can be eliminated.
However, conventional semiconductor devices, such as that of the above-sited patent document, have the following problems.
Since the upper chip is electrically connected to the substrate with wires, the wire bonding operation requires many steps. Further, since the wires and the upper chip are sealed with a resin in order to protect the wires, which are bent upward and downward and are loose, and the like, the thickness of the package increases by the height of the wire portions, and the like. Moreover, since use of a metal mold is necessary to provide the resin seal, the sealing operation requires many steps.